1. Field of the Invention
This invention relates to a heat-insulating engine with swirl chambers which includes main chambers at piston heads and swirl chambers at a cylinder head.
2. Description of the Prior Art
Swirl chambers of an engine with swirl chambers are described in Japanese Utility Model Laid-Open No. 21024/1984, for example. In this engine with swirl chambers, swirl chambers are provided to a cylinder head, swirl chamber blocks constituting the swirl chambers are made of a ceramic material as a whole, an air layer is defined in the major proportion of the fitting portions between the ceramic swirl chamber blocks and the cylinder head, the end portions of the fitting portions between the swirl chamber blocks and the cylinder head on the cylinder side are sealed gas-tight by a sealing material, and the fitting portions between the swirl chamber blocks and their insertion members are also sealed gas-tight by the sealing material.
Furthermore, a heat-insulating engine with swirl chambers has been developed to improve combustion of heat-insulating engines. For example, Japanese Patent Laid-Open No. 119616/1990 filed by the Applicant of the present invention discloses a heat-insulating engine with swirl chambers. In this heat-insulating engine with swirl chambers, swirl chambers equipped with fuel injection nozzles and having a heat-insulating structure are communicated with main chambers equipped with intake/exhaust valves by communication ports, control valves are disposed to open and close the communication ports, and the control valves open the communication ports near the end of a compression stroke of the engine so as to introduce at a stretch the intake air into the swirl chambers and close the communication ports during an intake stroke so as to inhibit the introduction of the intake air into the swirl chambers.
However, the problem with the engine having the swirl chambers is that when the combustion gas moves from the swirl chambers to the main chambers when the communication ports communicating the main chambers with the swirl chambers are throttled, a throttle loss occurs due to the communication ports and engine performance drops. On the other hand, the smaller the passage sectional area of the communication port, the higher the flowing speed of the vortex flow formed by the intake air introduced into the swirl chambers.
In engines with swirl chambers in general, forced stream of the combustion gas, that is, the flame, from the swirl chambers to the main chambers is limited to one direction. The outflowing speed at the initial stage of forced stream of the flame is high in the former half of flame blow-off if the pressure difference is great between the swirl chambers and the main chambers but drops in the latter stage of forced flame stream. Mixing with air existing in the main chambers needs a long time in this case, the combustion time becomes long, a fuel efficiency lowers and the drop of the outflowing speed results in the occurrence of hydrocarbons HC.
It is necessary in the heat-insulating engine with swirl chambers to elevate the combustion speed and to complete the combustion at an early stage. For, when a compression end temperature is higher by about 250.degree. C. than a cold engine as in the case of the heat-insulating engine, the viscosity of the compressed air increases and the fuel injected into this air cannot mix ideally with the air. On the other hand, an ignition delay of the fuel is small in a high temperature atmosphere and the fuel can be ignited within a time of about 1/5th of that of the cold engine. Therefore, the fuel and the air must be mixed instantaneously but the initial stage mixing and combustion of the air and the fuel are preferably carried out in the rich fuel-air mixture with a limited equivalent ratio and lean premixed combustion are preferably carried out in a diffusion combustion portion.